The present invention relates to a grinding machine which, mainly in the process of producing toothed belts, grinds the back surface of a molded and vulcanized cylindrical belt material (also called a slab) to finish the belt material thickness to the specified dimension before the belt material is cut into belts of a desired width. In particular, the present invention relates to a belt material grinding machine which is well suited to grinding relatively small-sized belt materials having a small diameter (less than 100 mm).
The following prior art grinding machines have been used until now as machines for grinding the back surface of a belt material for toothed belts having a diameter of 100 mm or more:
(1) Machines (see FIG. 7 and FIG. 8) wherein a cylindrical mold 61 for molding and vulcanization of a cylindrical belt material A' is held at the centers of both ends of the mold, together with the intact molded and vulcanized belt material A' covering the outer surface of the mold, between the rotation center 62 of a headstock and the rotation center 63 of a tailstock. The grinding is effected by turning the mold and the belt material A' and at the same time forcing a grinding wheel 64 or 65 rotating in the opposite direction at the contacting part with the belt material A', to contact the back surface of the belt material A'. Grinding machines of this kind include a traverse type grinding machine (FIG. 7) wherein a grinding wheel 64 which is narrower than the width of a belt material A', traverses, while turning, in the direction of the width of the belt material A', and a plunge cutting type grinding machine (FIG. 8) wherein a grinding wheel 65 of a width which is almost identical to that of the belt material A' merely rotates. PA1 (2) A centerless grinding machine (FIG. 9) wherein a mold 61 for molding and vulcanization, together with a cylindrical belt material A' covering the outer surface of the mold, is placed on a work rest 66, and then is held on both sides by a grinding wheel 67 and a regulating grinding wheel 68. When the mold 61 is rotated by the regulating grinding wheel 68, the grinding wheel 67 simultaneously rotates in the same direction at the contact part with the mold 61. PA1 (3) A grinding machine (FIG. 10) wherein a work roll 69 and a tension roll 70 are rotatably arranged with a space in between, the tension roll 70 being arranged to be actuated by a pneumatic cylinder (not illustrated) in a direction S for moving away from the work roll 69. A vulcanized cylindrical belt material A', after being removed from a mold 61, is held around the work roll 69 and the tension roll 70, and then the tension roll 70 is actuated by the pneumatic cylinder to tension the belt material A'. The belt material A' is rotated by the work roll 69 and the belt material A' on the work roll 69 is ground by a belt grinding machine 71.
In the cases of the traverse type and plunge cutting type grinding machines of (1) above, the mold used in molding and vulcanizing the belt material may experience thermal deformation when it is heated and then cooled during the vulcanization of the belt material. This, in turn, may result in the loss of circularity of the mold, or the dislocation of the points to be held by the rotation centers. It, therefore, is difficult to grind the belt material with the desired accuracy of thickness over its entire length.
The amount of grinding and the load during the grinding of a belt material are greater than those of conventional grinding of metal. Therefore, in the case of the centerless grinding machine of (2) above, the machine may experience, in addition to the above-mentioned problems of the grinding machines of (1), the dislocation of the axis of the mold and, in turn, vibration. It, therefore, is much more difficult to grind the belt material with the required accuracy of thickness.
In the case of the grinding machine of (3) above, to grind a cylindrical belt material for small-sized toothed belts having a diameter less than 100 mm (usually 29 to 100 mm), the diameters of the work roll and the tension roll should be around 15 mm. The width of a belt material before cutting, however, is normally about 450 mm. Therefore, when a tension is generated in the belt material by the pneumatic cylinder, the work roll and the tension roll will bend. Furthermore, under such a condition, if the grinding belt of the belt grinding machine is forced to contact the belt material on the work roll to effect the grinding, the work roll will be bent more towards the tension roll due to the grinding resistance. The resulting belt material will be uneven in thickness. The center portion, along the width direction of the belt material, will have a greater thickness than both ends of the belt material.
The present invention was made in view of the above-mentioned points. It is intended to provide a belt material grinding machine which is particularly suitable for grinding the back surface of small-sized toothed belt materials having a diameter less than 100 mm, and also is capable of grinding a wide belt material, under conditions very close to the service conditions of the belt, to achieve a constant thickness along the width of the belt material, thus producing a belt material with a high accuracy of thickness.